In the construction industry, levels are used to ensure that structural members are installed in their exact intended orientations. Common construction levels include plural vials to indicate at least horizontal and plumb (vertical) orientations. In addition to a centrally-positioned vial, most levels include at least one other vial positioned within the frame of the level away from the center. Because such other vial(s) can be viewed only from either side of the frame, it is desirable to provide a clear and open view of the vial which provides easy reading thereof.
A number of prior levels have so-called block vials installed at within-the-frame positions such that they are viewable from the side of the frame. While such block vials provide good protection for the vial, manufacturing of such block vials involves complicated techniques, including complicated machining of the interiors of block-vial interiors which increases the cost of level manufacturing. Since block vials typically have a substantially rectangular outer shape and are installed in a round opening within the frame of the level, the sides of such rectangular block interfere with light rays and reduce clarity in vial reading. Further, the space between the rectangular vial sides and the edges of the level-frame openings tends to become foggy or collect dust which further decreases the vial clarity and detracts from the overall quality of the level.
Some prior levels, such as those disclosed in U.S. Pat. No. 786,269 (Curry), U.S. Pat. No. 4,124,940 (Vaida) and U.S. Pat. No. 4,991,303 (Marth et al.), have attempted to secure substantially cylindrical vials to the level frame. However, such prior installations have multiple shortcomings which negatively effect the quality of the levels and visual characteristics of the vial.
For example, in the Curry patent the vials are secured within a vial holder by filling gaps around the ends of the vial with plaster-of-paris or other suitable material which remains visible when the vial holder is installed within the frame of the level. Such materials for securing the vial to the holder require special handling for accurate and clean application to produce good appearance. This results in higher cost and problems with respect to vial appearance and overall level quality.
In the Vaida level, half of the vial holder is first secured to the level frame and then the other vial-holder half, with a cylindrical vial mounted therein, is rotationally secured to the first half. This assembly requires secure engagement between the vial and the second half of the vial holder, and secure engagement typically involves certain configurational features for the vial and the second vial-holder half. Such features create multiple light-interfering structures about the vial, and this degrades overall visibility of the vial itself. Furthermore, the rotational relationship between the halves dictates positioning of the vial substantially fully within the second half of the vial holder and off the center of the frame of the level. This compromises visibility of the vial from one side. In addition, installation of the open vial casing to the level frame allows a probability of contamination of the interior of the holder, which results in degrading the space around the vial and, over time, reducing reading clarity of the vial itself.
Similarly, in the Marth et al. patent, a open two-half vial case is secured to the frame by sandwiching the vial and the frame between the case halves. Thus, the case interior is prone to contamination during handling and installation. Furthermore, the accuracy of the vial orientation in the Marth et al. patent is dependent on precision of an octagonal vial opening and precision in forming the octagonal vial case. Finally, such octagonal shape, which is critical for the vial casing of the Marth et al. patent, by its nature has multiple differently-angled surfaces which reflect and bend light rays, thus decreasing clarity of observation of the vial.
In the field of high-precision measuring and sensing instruments such as construction levels, quality and visual clarity are matters of great importance. There is a need for an improved level which overcomes the aforementioned problems; more specifically, there is a need for an improved cylindrical-vial mounting structure that provides improved and lasting clarity of the vial and the visibility through the vial opening about the vial for easy and clear reading of the vial.